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L0301P7 - Fuel Molecules Part 1
Metabolic Pathways *all interrelated *a series of small steps *all catalysed by specific enzymes *often compartmentalised (occurs in a specific place in the cell) *highly regulated (feedback systems) Energy and Electrons from Glucose C6H12O6 + 6O2 —> 6CO2 + 6H2O + energy *same equation applies to metabolism of glucose by the cells however the reaction is accomplished in a series of steps *energy produced is captured as ATP Cellular Respiration Aerobic Metabolism *in presence of oxygen = complete oxidation *much more efficient *waste products: H2O and CO2 *32 ATP Anaerobic Metabolism *when oxygen is not present = incomplete *waste products: lactic acid, ethanol, CO2 *2ATP Many metabolic processes are oxidation-reduction reactions = transfer of electrons Coenzymes *nonprotein carbon containing molecules *move from enzyme to enzyme by adding or removing chemical groups *are not permanently bound *are changed by the reaction and released from the enzyme NAD+ and NADH *coenzyme - key electron carrier *NAD+ - oxidised form - nicotinamide adenine dinucleotide *NADH - reduced form *electron carrier in biological redox reactions *ratio of NAD+ to NADH regulates rate of reaction Glycolysis *substrate: glucose *breaking down of glucose into pyruvate *occurs in the presence or absence of O2 *occurs in the cytoplasm of the cell *pathway of 10 enzyme catalysed reactions *note: however other monosaccharides can be fed into glycolysis after being converted in to glycolytic intermediates Preparatory Phase *endergonic *steps 1-5 *uses 2 ATP **one in step 1, one in step 3 *6C molecule into 2 3C molecules **one glyceraldehyde 3-phosphate and one dihydroxyacetone phosphate (an intermediate) **which is converted to glyceraldehyde 3-phosphate Pay-off Phase *exergonic *steps 6-10 *produces 4 ATP **two in step 7, two in step 10 *produces 2NADH Results *2 pyruvate *2 NADH *2 ATP Fate of Pyruvate *depends on the presence of oxygen **present - aerobic respiration **absent - fermentation Under Aerobic Conditions *after glycolysis and before citric acid cycle *if oxygen is present, pyruvate is converted to acetyl CoA¹ (reversible reaction) *one NADH produced *occurs in the mitochondria (matrix) *enzyme: pyruvate dehydrogenase **highly regulated **has five cofactors, including: ***NAD+ ****derived from B group vitamin ***Coenzyme A ***FAD ****flavin adenine dinucleotide ****derived from riboflavin ***TPP ****thiamin pyrophosphate ***thiamin ****B group vitamin ****enormous multicomplex enzyme ¹Acetyl CoA can also be used for: *synthesis of fatty acids *synthesis of cholesterol *synthesis of non-essential (can be produced in body and does not have to be ingested) amino acids Under Anaerobic Conditions *fermentation occurs **occurs in the cytoplasm *pyruvate reduced to NADH to form lactate *enzyme: lactate dehydrogenase *2NADH converted back to 2NAD+ therefore it can sustain glycolysis Metabolism of Fats Triglycerides *most of the fats in the body exist in this form *fatty acids are cleaved from the glycerol in the gastrointestinal tract during digestion *fatty acids can be repackaged to be stored or used to create energy β-Oxidation of Fatty Acids *occurs in the mitochondria *no ATP produced, just produces intermediate Acetyl CoA for CAC Process #2C units (acetyl CoA) cleaved #acetyl CoA enters the citric acid cycle #production of NADH and FADH2 #*number = number of acetyl CoA - 1  = (number of C in fatty acid ÷ 2) - 1 Fate of Glycerol *glycerol converted to an intermediate of glycolysis = dihydroxyacetone phosphate *energy can be released via glycolysis and the citric acid cycle *used for gluconeogenesis Ketone Bodies *acetyl CoA formed in the liver during β-oxidation of fatty acids can be converted to ketone bodies *exported to other tissues to be used as an extra source of energy *normally only small amounts are made **i.e. acetone, acetoacetate, β-hydroxybutyrate *severe starvation or untreated diabetes mellitus = overproduction of ketones = ketoacidosis Catabolism of Ketone Bodies *livers way of providing energy *efficient source of energy *tissues such as brain, skeletal & heart muscle can use ketones *converted into acetyl CoA and oxidised via the CAC and ETC to provide energy